Satellite routing protocol with dynamic IP addressing

ABSTRACT

A method for establishing routing for communications using a satellite in a Demand Assigned Multiple Access (DAMA) Wide Area Network (WAN) is disclosed. In one step, Routing Information Messages (RIMs) are received from a plurality of subscriber terminal (ST) nodes at a Network Control Station (NCS). A network map of Internet protocol (IP) network prefixes reachable via the DAMA WAN is constructed using the RIMs. A bandwidth constricted control channel is allocated using the satellite. At least one control channel message is sent over the bandwidth constricted control channel to at least one ST node coupled to the WAN.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 09/822,966 filed Mar. 29, 2001, which claims thebenefit of U.S. Provisional Patent Application No. 60/196,054 filed Apr.10, 2000.

BACKGROUND OF THE INVENTION

This invention relates to packet-switched communications via satellitelinks. A class of communication networks employ packet-switched routing.Typically, linking is established by local communication paths and localtraffic management in which the traffic management mechanism is only incommunication with those nodes through which traffic is actively passed.Traditional routing approaches are unable to discover routes to nodesfor which there is no current active connection. In a demand assignedsatellite network, a node may be directly connected to any other node,upon request, but may only be able to support a small number ofconnections at any time. A mechanism is needed for finding routes, andoptimizing routing where dynamically changing links such as a demandassigned satellite link are in the path.

Definitions

The following defined terms are used herein.

General Definitions

Client/Server—A server is any computer that has some function requestedby a number of other client computers. It is a basic assumption thatservers have fixed IP addresses.

A single computer can handle a number of server functions. A computercan be a server for certain services and a client for other services.

Mobile network—The collection of processors, routers, servers andmiscellaneous LAN equipment which are physically connected together toperform various data acquisition functions. A mobile network shares acommon IP network (or subnet) address amongst its computing resources.Mobile networks, as the name implies, may change physical location andaccess other networks via standard terrestrial connections or viasatellite.

Remote Terrestrial LAN—A LAN connecting mobile networks to othernetworks via terrestrial links.

VSAT LAN—A separate LAN connecting resources at a gateway site to theGateway VSAT (Very Small Aperture Terminal) equipment.

Gateway WAN—The set of WAN connections which link the various local LANsto the VSAT LAN and to the Remote Terrestrial LAN.

IP Router—A device that routes IP (Internet Protocol) packets betweeninterfaces based on the IP destination address.

Remote ST—A VSAT Subscriber Terminal (ST) located at remote locations.The remote ST is responsible for interfacing to telephony and IP devicesat remote sites. The remote ST acts as an IP router, relaying IP packetsbetween the LAN at the remote site and the satellite WAN.

Gateway ST—A VSAT Subscriber Terminal (ST) that terminates IP or voicetraffic into the terrestrial network. The Gateway ST acts as an IProuter, relaying IP packets between the VSAT LAN at the gateway and thesatellite WAN. Consists of Local ST and integrated MAR.

Terrestrial Router—An IP router that relays IP packets between the VSATor Remote Terrestrial LAN.

NCS—Network Control Station. The VSAT NCS controls a VSAT network,providing resource configuration, scheduling, and management functionsto the network operator(s). Implements the network control system.

Server and Router Definitions (Fixed IP Address Assignment)

All of the following computing resources are considered servers orrouters. These types of resources require pre-assigned, fixed IPaddresses. Without this assumption, it would be difficult to manageapplications in the IP network.

Application Server (AS)—Computer that runs applications specific to alocal operation. These computers may be at mobile or fixed sites.

DNS (Domain Name Service) Server—Handles Domain Name resolution.

WINS Server—Handles Windows Named Services.

DHCP Server—Any computer running the DHCP service. May be located atfixed or mobile sites.

Mobile Boundary Router (MBR)—Any router connected between the RemoteTerrestrial LAN or VSAT LAN and the rest of the network. The purpose ofthe MBR is to act as the interface between mobile network elements andthe rest of the network. The MBR will also convert routing informationreceived from the VSAT and Remote Terrestrial LANs into routinginformation for the rest of the network.

Mobile Area Router (MAR)—Any router located between the RemoteTerrestrial and/or VSAT LAN and mobile networks. The purpose of the MARis to advertise reachability to the mobile networks. All packets betweenthe mobile and the gateway WAN network traverse through a MAR.

Client Workstations, Real-Time Computers: Dynamic/Non-Global IPAddressing

All of the following computing resources have dynamic IP addressing ornon-unique IP addresses.

Client Computer (CC)—Computers that only run ‘client’ applications.These computers may obtain their addresses dynamically, or they may bestatically defined. For dynamic addressing, they will use DHCP.

Subscriber Terminal (ST)—The VSAT nodes each have a unique address, as amember of the LAN to which they are connected.

IP and Routing Definitions

IP—Internet Protocol.

IP address—A 32-bit address, usually specified in 4 decimal numbers,separated by periods. For instance, 192.168.1.5 is a 32-bit IP address.

IP network—A full range of IP addresses, defined by the IP networkaddress class. Any node with an IP address in the network range is amember of the IP network. Originally, IP addresses were divided intoClass A, B, C, D, and E networks. These different classes defined thenumber of bits allocated to the ‘network’ portion, and the number ofbits allocated to the ‘host’ portion. Class A networks have an 8-bitnetwork portion, and a 24-bit host portion, Class B networks have 16/16,and Class C networks have 24/8.

IP subnet—To conserve the IP address space, IP networks were subdividedinto subnetworks, or subnets, by using portions of the host field as asubnet field. A subnet mask is used to define how many bits are includedin the IP subnet.

IP network prefix—The concepts of IP networks and subnets have beencombined into a common term of a network prefix. A network prefix isthat portion of an IP address which would be selected by a subnet maskwhose most significant bits are ones and the rest are zeros. Networkprefix will be used in this document instead of the older IP network andIP subnet terminology.

ICMP—Internet Control Message Protocol, an extension to the InternetProtocol (IP) defined by RFC 792. ICMP supports packets containingerror, control, and informational messages.

RIPv2—Routing Information Protocol, version 2. A protocol defined by RFC1058 that specifies how routers exchange routing table information. WithRIP, routers periodically exchange their entire routing tables. RIPv2can be used as the routing protocol between the gateway and—MBR in thiscontext.

OSPF—Open Shortest Path First is a routing protocol developed for IPnetworks based on the shortest path first or link-state algorithm. OSPFversion 2 is described in RFC 2328.

DHCP—Dynamic Host Configuration Protocol, a protocol for assigningdynamic IP addresses to devices on a network. With dynamic addressing, adevice can have a different IP address every time it connects to thenetwork.

Route Summarization—Process whereby a router accumulates a set of routesinto a single route advertisement.

NAT—Network Address Translation, a function that converts host addressesin IP packets that traverse two networks. NAT is used to preserve IPaddresses assigned to hosts, when those hosts addresses do not match theIP network prefix of the LAN for which this host resides.

DNS—Domain Name System (or Service), an Internet service that translatesdomain names into IP addresses.

WINS—Windows Internet Naming Service, a system that determines the IPaddress associated with a particular network computer. This is calledname resolution. WINS supports network client and server computersrunning Windows and can provide name resolution for other computers withspecial arrangements.

DAMA—Demand Assigned Multiple Access, the process of automaticallyallocating communications resources (in this case satellite bandwidthand power) based on real-time demand.

DAMA IP—The VSAT function that automatically sets up and tears downlinks on demand, based on the contents of the IP packets that are beingrouted.

Scheduled IP—The VSAT function that sets up and tears down links on aschedule managed by the NCS.

Definitions Introduced According to the Invention

The following definitions are introduced at this point for convenienceand represent new features in accordance with the invention.

SRP—Satellite Routing Protocol, a VSAT specific protocol for extendingthe IP routing information over a VSAT WAN, in order to permit mobility,and automatic network reconfiguration.

DAMA VSAT WAN—A WAN implemented via a satellite network using SRP.

RIN—Routing Information Notice message of a mobile Network, as relayedto an NCS by a remote ST over the DAMA control channel

RIN Request—NCS message requesting RIN from an ST.

RIS—Routing Information Summary, an NCS message sent to STs indicatingrouting table update.

TRIN—Terrestrial Routing Information Notice, a message sent from an STto indicate routes available to terrestrial networks.

TRIN Request—NCS message requesting TRIN from an ST.

TRIS—Terrestrial Routing Information Summary, a message sent from theNCS to STs to indicate terrestrial routing.

RR—Routing Request, a message sent from an ST to request routinginformation for a given IP packet.

RN—Routing Notice, a message sent from an ST in response to an RR,indicating that this ST can route a packet specified in the RR.

Limitations of Prior Art Terrestrial-Oriented IP Routing Protocols

A routing protocol is needed to communicate between subscriber terminals(STs) in the Demand Assigned Multiple Access (DAMA) network. While thestandard Internet routing protocol RIPv2 is adequate for use in the LANenvironment, it has problems for use over the DAMA network. Some ofthese limitations will be discussed here, along with a discussion onworking groups that are working on similar problems.

RIPv2 achieves stability by sending out routing packets every 30seconds, regardless of whether any routing information has changed. Thiscauses needless information to be sent between all DAMA sitesparticipating in IP routing. RFC 1581 specifies changes that can be madeto RIPv2 in support of demand circuits. Essentially, RIP routing packetsare NOT sent between routers if the link between the routers is known tobe good, and no routing information has changed. This is applicable topoint-to-point WAN environments, not a DAMA WAN environment. It isactually desirable to get some notification from neighboring STs, toensure the ST is online. However, this packet can be a ‘hello’ packet,and does not need to contain redundant routing information that isunchanged since the last update message.

RIPv2 advertises all routes it has learned from other attachedinterfaces. In our case, this means that RIPv2 running on the LAN canpick up IP routes that then need to be sent to all DAMA nodes in thenetwork. Assume that there are 100 DAMA nodes, each possessing 10 routeseach. This would require 1000 routing entries to be sent out every 30seconds. 1000 DAMA nodes would require 10,000 routes every 30 seconds.Clearly, this approach will not scale well. One solution is to back offfrom the 30 second update rate, but that has the side effect of slowingdown route convergence.

It is highly desirable to fit IP routing packets into small controlmessages. Minimizing the size of IP routing messages is needed to allowthe system to scale.

Finally, certain centralized events require the VSAT subnets to bemobile. These mobile subnets will move around, and be very transitory. Agiven mobile network may be online for a day, a week, or longer. Thesechanges must be communicated effectively via the DAMA network.

SUMMARY OF THE INVENTION

According to the invention, a satellite routing protocol is provided ina packet switched mesh network environment (i.e., where user traffic isnot routed through a single or central node) wherein all IP planning androuting in the global WAN network is provided through a central databasemanagement element and routing information is disseminated separatelyfrom the communication traffic via a bandwidth constricted controlchannel in communication with each node but typically set aside forother purposes (such as conventional DAMA control). Two specificapproaches include a link state approach and a distance vector approach.The specific embodiments disclosed for the Satellite Routing Protocol(SRP) system according to the invention allows both fixed and mobilenetworks to connect directly to each other or to a gateway network viaeither a terrestrial LAN or a Demand Assigned Multiple Access (DAMA) WANwhere there are links that are dynamically assignable.

The following detailed description defines a representative SatelliteRouting Protocol (SRP), which is a VSAT DAMA IP routing protocol. Theinvention will be better understood by reference to the followingdetailed description in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the major components of the mobile networkaccording to the invention.

FIG. 2 is a diagram showing various device types and a router.

FIG. 3 illustrates a configuration of VSAT units.

FIG. 4 depicts IP routing protocols according to the invention, togetherwith the equipment that participates in forwarding IP packets betweencomputing resources.

FIG. 5 depicts the interaction between the components in the system.

FIG. 6 shows the process that occurs when an IP circuit is brought up.

FIG. 7 shows the process that occurs when an IP circuit is brought upvia the NCS scheduler.

FIG. 8 shows the process of normal ST network entry and exit using adistance vector approach.

FIG. 9 shows the process of normal ST network entry and exit using linkstate approach.

FIG. 10 shows the process that occurs when the NCS loses and regainscommunication with an ST using a distance vector approach.

FIG. 11 shows the process that occurs when the NCS loses and regainscommunication with an ST using a link state approach.

FIG. 12 shows the process that occurs when there is a checksum mismatchusing the link state approach.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Network Diagram

FIG. 1 is a diagram of major components of a network environment 10 inwhich the present invention may be implemented.

Mobile networks 12, 14, 16, 18, 20 may be connected to a gateway WAN 22network via a VSAT DAMA WAN 24 or a Remote Terrestrial LAN 26. Thelocation of a given mobile network can change geographically, but the IPnetwork prefix assigned will remain the same. DHCP and NAT services (notshown) may be used on the Mobile Nets 12, 14, 16, 18, 20 in order tosupport this mobile movement of computing resources. The use of thesetwo services, and the IP routing involved, will be discussedhereinafter.

In accordance with the invention, a set of IP network prefixes isassigned to support networks reachable via the VSAT DAMA WAN 24.Additionally, a set of IP network prefixes is assigned for the RemoteTerrestrial LANs 26. These networks are typically permanently assigned,so that a Mobile Boundary Router (MBR) at a VSAT LAN 32 and the MARs 34,36 at the Remote Terrestrial LAN 26 are able to continually advertisethose IP networks as reachable via their respective MBRs 30, 31. Thisminimizes routing changes propagated throughout the rest of the gatewayWAN network 22.

The MBRs 30, 31 connect the VSAT LAN 32 and Remote Terrestrial LANs 26to the rest of the gateway WAN network 22. MBRs advertise routinginformation into another network typically using OSPF or other protocol.MBRs translate routing information, such as RIPv2 and OSPF routinginformation, and can import from one area to another, such as the RIPv2routing information into the OSPF area.

Computing resources that connect to the mobile environment have IPaddresses predefined, or assigned via DHCP. Three cases of IP addressingare possible, but the result must be that IP packets originated by amobile computing device MUST have a valid VSAT or Remote Terrestrial IPnetwork prefix. The three cases, called Types 1 through 3, are discussedhere briefly.

Type 1 computing resource will run DHCP and obtain its IP address from aDHCP server. The DHCP server will allocate IP addresses that areconsistent with the IP network prefix assigned for this particular LAN.

Type 2 computing resources are pre-assigned an IP address that isconsistent with the IP network prefix assigned for this particular LAN.This may occur to support the current environment, or to support servers(such as the DHCP server) that need to have a predefined IP address.

Type 3 computing resources are pre-assigned an IP address that is notconsistent with the IP network prefix assigned for this particular LAN.This will occur if ‘legacy’ equipment needs to be used at a site, andthe IP address can not be easily changed (or DHCP enabled). In thiscase, NAT will be used to translate a legacy address to a correct VSATor Remote Terrestrial LAN IP address. NAT will run on routers installedat the Remote Terrestrial location, and at remote sites that need tosupport legacy equipment.

In accordance with the invention, an enhanced network control system(NCS) 35 is provided in conjunction with the VSAT DAMA WAN 24 to managethe satellite resources to maximize traffic throughput and otheroperations in accordance with the protocol of the invention. The NCSemploys the bandwidth constricted control channel 36 of the conventionalDAMA protocol to communicate control information via the relay satellite39 to all resources monitoring the control channel. The resourcesinclude all STs having active traffic or which can receive signals,whether or not currently active. (It is assumed that STs can onlycommunicate with each other via a DAMA WAN when they can mutuallyreceive signals from the DAMA NCS controller 35 over the satellite 39.)

Referring to FIG. 2, there is shown a diagram of a typical mobile nethaving a NAT router 38. NAT routers 38 have two LAN interfaces 40, 42.Type 1 devices and Type 2 devices connect to the primary LAN interface40, while Type 3 devices connect to the secondary LAN interface 42. Theprimary LAN interface 40 connects via an MAR router 34,36 (FIG. 1 or 2)to the remote terrestrial LAN 26 or via a remote Subscriber Terminal(ST) 44, 46 or 48 (FIG. 1) and thence via the VSAT DAMA WAN 24 and afurther remote ST/MAR router 50 or 52 to the VSAT LAN 32.

Supporting both NAT and DHCP services allows central controllers (notshown) to transition their mobile computing resources as time permits.Also, resources may be deployed dynamically at any remote VSAT location,or connected to a LAN at any Remote Terrestrial location. The usersimply needs to connect to the proper LAN (NAT or DHCP LAN) so thataccess to the gateway WAN network 22 is enabled.

Mobile Network Operations

The remote STs 44, 46, 48 are responsible for providing connectivity fortheir own mobile networks 12, 14, 16 to any of the other networkresources such as the rest of the gateway WAN network 22, as for examplevia the VSAT DAMA WAN 24 and the VSAT LAN 32. The remote STs typicallyobtain their IP address (and associated subnet mask) from a DHCP server.Upon obtaining their unique IP addresses, the remote STs are operativeto advertise that their portion of the IP network available at theirrespective mobile network sites, using the Satellite Routing Protocolaccording to the invention.

The typical remote ST 12 executes a portion of the SRP in communicationwith the NCS 35. Once online, the remote ST sets up and tears down DAMAIP links based on its local application demand, as describedhereinafter. Additionally, the NCS 35 may initiate IP links based on aschedule developed around reservations inputted by the system humanoperator. IP links also may be initiated by local STs 50, 52 based onlocal demand.

Remote Terrestrial LAN

The Field LAN or Remote Terrestrial LAN 26 may have a single router ormany routers. This is determined by the number of LAN ports desired atthe Remote Terrestrial LAN and the type of router chosen for centralizedcontrol, such as MBR router 31. It is the responsibility of the systemdeployer having centralized control to determine the needs of the RemoteTerrestrial LAN 26.

VSAT Gateway Operations

VSAT Gateway equipment is used to access all mobile networks of thesystem 10 that use the VSAT DAMA WAN 24. Referring to FIG. 3, the VSATGateway equipment typically includes VSAT units 148-150 (typicallyracked together) connected to the VSAT LAN 32. The STs 148-150 arecoupled through hub RF equipment 158 to the satellite antenna.

The VSAT units shown in FIG. 3 serve two functions. One is to provideaccess to the mobile networks over the VSAT WAN. Modem resourcesresident within the VSAT equipment are dynamically allocated as neededto serve the bandwidth requirements of each mobile network. Second, theVSAT units perform the MAR function, advertising reachability to thegreater network environment 10 connected to the VSAT LAN 32, typicallythrough the MBRs 30, 31.

In order to efficiently use all available resources at the gateway, thesatellite modems are logically grouped into pools at the NCS 35. When agiven mobile network 12, 14, 16 requires IP connectivity over the DAMAWAN to another network, the NCS simply assigns an appropriate availableDAMA modem from any of the VSATs located at the gateway.

IP Routing

FIG. 4 depicts IP routing protocols involved with the Satellite RoutingProtocol 124 in a typical embodiment according to the invention, as wellas the equipment that participates in forwarding IP packets betweencomputing resources. The protocols are depicted as “clouds” betweenelements of the system 10. It is to be noted that packets that traverseover the DAMA network are routed, not bridged.

The gateway WAN network is based on OSPF 122 and may contain over 100routers. The network may easily span multiple countries and contain anumber of geographic areas.

The SRP protocol 124 ties into the OSPF protocol network at gatewaysites 50, 55, comprising what is called local STs with MAR routerswherein the MAR routers service the interface of the SRP protocol withother protocols (FIG. 1). Although only one gateway ST is shown at asingle site in FIG. 4, there are generally a number of gateway STsconnected to a single MBR 30 or 33 at a given gateway site, as shown inFIG. 1. The protocol used between the Gateway STs 50 or 55 and the MBR30 or 33 is typically RIPv2 132.

RIPv2 132 or other appropriate gateway-MBR protocol serves two mainfunctions. The first function is to advertise the IP network prefixescurrently active at the mobile sites. As remote STs enter and leave theDAMA network, these changes are typically communicated via RIPv2. Theywill in turn allow the MBR 30 or 33 to determine whether to routepackets from the OSPF protocol-based network into the gateway-MBR-basednetwork, or whether to generate an ICMP message back to the source,signifying that the targeted network is “unreachable.”

The second function of the gateway-MBR protocol 132 such as RIPv2 is toroute packets to the appropriate gateway ST 50 or 55. As IP links areactivated and terminated between gateway STs and remote STs 44, 46, 48,the gateway-MBR protocol 132 (RIPv2) is used to “steer” the IP packetsfrom the MBR to the appropriate gateway ST that has the active links.There are generally more remote STs than modem resources available atthe gateway STs 50, 52. Therefore the choice of which gateway ST is usedto connect to a given remote ST can change over time. The gateway-MBRprotocol metrics may be used to ensure the MBR picks a “best path,” inaccordance with the invention to the remote IP network prefix location.

According to invention, there are two approaches to the implementationof the inventive SRP as a DAMA-based routing protocol, as depicted inFIGS. 8 and 9. These are the distance vector approach and the link stateapproach. In both cases, the main function of SRP is to advertise the IPnetwork prefix of the LANs directly connected to the STs. In theprevious network diagram, this would consist of mobile networks such asM1.0, M2.0, and so on. Additionally, the IP network prefix of anygateway locations is also advertised by SRP.

Because the SRP has a compact and efficient messaging scheme, asdescribed herein, SRP operates over existing control channels present ina DAMA network. Therefore, SRP does not require additional modems oradditional modem modes in order to operate, which is a distinctadvantage according to the invention. FIG. 5 depicts the interactionbetween the components in the system. It is a timeline serving as anoverview of system operation. The messages of SRP according to theinvention are depicted by labeled vectors between the nodes as listed atthe top of the figure, and time is a vertical axis. This diagram is inaccordance with accepted industry descriptive documentation practicesand requires no further explanation to those of ordinary skill in theart.

The protocol includes a Remote ST Login, which is an ST login thatcauses initial routing information to be sent to the NCS upon initiationof the remote network. The login information is forwarded to all STs inthe network. Gateway STs intercept and interpret this information andperform a RIP routing update message, including the new IP network nowreachable via this new remote ST. The NCS also stores the IP networkprefix for this remote ST. This is used by the NCS later when performing“next hop” resolution.

During normal operation, there are periodic SRP updates where the NCSperiodically polls each ST for basic routing information via the RINrequest message. As required, this routing information is sent to therest of the STs in the network.

Remote ST Logout is also provided. The ST may log out due to operatoraction at the ST. This logout event will eventually cause gateway STs totimeout and stop advertising the IP network prefix associated with theremote ST that logged out.

Remote mobile network sites are considered “stub” networks, that is, norouting protocols are run at the remote locations. The LANs 12, 14, 16of FIG. 1 are each simple, single IP network prefix networks, and theprotocols 112, 114, 116 of FIG. 4 do not contain routing features.

As discussed previously, it is possible that legacy devices may existwhose IP network prefix does not match the IP network prefix of theremote ST. These devices would not be able to access the Gateway WANnetwork but for this invention, since their packets would not be routed.To solve this problem, a Network Address Translation (NAT) device 38(FIG. 2) converts the legacy addresses into the proper IP networkprefix, allowing the packets to be routed.

DAMA IP

When an IP packet is transmitted by a network node, it traverses the IPnetwork one hop at a time until it arrives at its ultimate destination.Devices that forward IP packets are called routers or switches. The VSATSTs operate as SRP routers. When an ST receives an IP packet, it firstvalidates if this packet can be routed. If not, the packet is droppedand an ICMP “unreachable” message is sent back to the source.

FIG. 6 shows the process that occurs when an IP circuit is brought up inthe SRP using the NCS.

First is the IP request. This occurs when the Remote ST receives an IPpacket whose destination address matches a route entry in this ST'srouting database. An IP request is sent with the next hop addressdetermined from the STs local routing table to the NCS for processing.

Second is the IP Assignment when the NCS reviews the next hop addresscontained in the request to determine the possible destination STs thatmay be used to terminate this request. The NCS compares the IP networkprefix sent in the IP request to the IP network prefix assigned to theSTs that are logged into the network. If the IP network prefix is found,the NCS selects an available modem to satisfy the request, whichselection is embedded in the IP Assignment message. Note that local STsin the same gateway share the same IP network prefix, and the NCSautomatically puts these STs into a “pool” of resources to select fromfor that given IP network prefix.

If modem resources are available, the NCS then checks for availablebandwidth and power to meet the needs specified in the IP request. Ifadequate resources are available, the NCS sends out the IP Assignmentmessage (a control message) to the remote ST and to the Gateway STassigned to service this remote ST for this IP request.

The MAR portion of the Gateway ST assigned to service this IP networkthereafter sends out RIP packets with a metric that causes the MBR toroute packets to this requesting ST, instead of one of the other STs inits pool. Traffic packets are then sent over the DAMA IP traffic linkdescribed in the IP Assignment message to the targeted remote ST.Packets sent by computing resources at the remote ST site use the DAMAIP traffic link to transmit data to the gateway ST, which forwards theIP packets to the MBR.

A Periodic RIP Update occurs when the Gateway ST continues to advertisereachability to the specific IP network prefix at a periodic interval.

IP Teardown occurs at some point when the activity timer triggers the IPtraffic link to be torn down. Either the remote ST or the Gateway STinitiates this activity. The result is that the modem, satellitebandwidth, and satellite power resources are freed up, and the GatewayST advertises a metric consistent with the other STs in its pool, thusstopping advertising that this is the preferred path to the IP networkthat was best reachable via the active DAMA IP traffic link.

Other Scenarios

Other scenarios are not specifically illustrated.

1) Gateway ST initiates request. This scenario would show the initial IPrequest event originating from the gateway ST. The remainder of the dataflow is the same.

2) Remote ST to Remote ST. This scenario would involve no RIP updates,since RIP is not run at remote locations.

Scheduled IP

FIG. 7 shows the process that occurs when an IP circuit is brought upvia the NCS scheduler. The NCS initiates IP circuits per the scheduledefined by the operator. If modem resources are available, the NCS thenchecks for available bandwidth and power to meet the needs specified inthe IP request. If adequate resources are available, the NCS sends outthe IP Assignment to the remote ST, and to the gateway ST assigned toservice this remote ST.

The Gateway ST assigned to service this IP network sends out RIP packetswith a metric that will cause the MBR to route packets to this STinstead of any other ST in its pool. These packets are then sent overthe DAMA IP traffic link to the specifically addressed remote ST.Packets sent by computing resources at the remote ST site use the DAMAIP traffic link to transmit data to the Gateway ST, which forwards theIP packets to the MBR. The Gateway ST continues to advertisereachability to the specific IP network prefix at a periodic interval.This is again a Periodic RIP Update.

The NCS terminates the IP traffic link at the time defined in theschedule via the IP Teardown message. The result is that the modem,satellite bandwidth, and satellite power resources are freed up, and theGateway ST stops advertising that this is the preferred path to the IPnetwork that was best reachable via the active DAMA IP traffic link.

The Satellite Routing Protocol (SRP) according to the invention hasthree main functions. The primary function of the SRP is to build thenetwork map of all directly connected IP network prefixes reachable viathe DAMA WAN. Each ST advertises the IP network prefix of its LAN usingthe Routing Information Notice (RIN). The NCS is responsible for pollingeach ST for its RIN at a periodic rate. The NCS uses this information tosend out Routing Information Summaries (RIS) to the rest of the STs inthe network. RINs are used to keep all STs aware of the other STsconnected to the DAMA network, together with their directly-connectednetwork prefixes. If route summarization is being used on the network,this route summary information is also disseminated via RIN/RISmessages. Part of the construction of the network map is routesummarization. Route summarization, the process whereby a routeraccumulates a set of routes into a single route advertisement, can bedone when a number of IP subnets reachable by a given router arecontiguous and span across an area that can be defined by an IP subnetmask. For instance, suppose a standard class C network, 199.106.52.0,was partitioned into four subnets. This would be 199.106.52.0,199.106.52.64, 199.106.52.128, and 199.106.52.192. If a router can reacheach of these subnets but does not support route summarization, it wouldhave to advertise four separate routes. Each of these routes would carrythe IP subnet address, and a 26 bit subnet mask. With routesummarization according to the invention, a single route would beadvertised, 199.106.52.0, with a 24 bit subnet mask.

A second function of the SRP according to the invention is to allowspecific STs to advertise routing information beyond that of itsdirectly-connected network. For instance, if an ST is running RIPv2 andlearns of routes available via other routers, this routes availableinformation is forwarded to other STs using the SRP according to theinvention. The STs send this additional routing information to the NCSusing the Terrestrial Routing Information Notice TRIN. The NCS then usesthis information to generate Terrestrial Routing Information SummaryTRIS, which is sent to all STs in the network.

A third function of the SRP according to the invention is to probe forother IP network prefixes reachable via the DAMA network. It uses aquery/response process as follows. The process is initiated when an ST,herein a requesting ST, receives an IP packet that cannot be routeddirectly, but which matches the ‘supernet’ defined for one of the otherSTs in the network. The requesting ST then generates a Route Request(RR) message, which is sent to all STs in the DAMA network. The RRmessage contains the IP destination address from the IP packet that therequesting ST is trying to route, prompting each ST to search itsrouting table to determine if it can route the IP packet as desired. Ifso, the routing capable ST sends a Route Notice (RN) message back to therequesting ST. The requesting ST then enters a route for this IP subnet,triggering a DAMA IP link request to the target ST.

SRP according to the invention supports route summarization, and it isused in two ways. The first use is to support the standard use of routesummarization, that is, to minimize the number of routes that must beadvertised. SRP supports this inherently by sending the IP networkprefix address, along with an associated subnet mask. The second use isto support proper operation of the route query process.

To understand the route query process, a brief discussion of theoperation of routing must be described. When an IP packet is received bya router, it determines first whether the packet is destined for itself.If so, the packet is sent up to a higher layer protocol, such as TCP orUDP. If the packet is not destined for the router, then an attempt ismade at forwarding the packet out one of the router's interfaces. Therouter checks its route table to determine if this IP packet isforwarded, using the destination IP address contained in the IP packet.

The router attempts to make the ‘best’ match for the destinationaddress. The rules it uses are reasonably standard as follows.

1) First, check if there is a host route that matches the full 32-bitaddress of the destination IP address. If a match is found, route thepacket to the next hop defined for the host route.

2) If the host route check fails, determine if this IP address issubnetted. If so, search the route table looking for a match to the mostqualified subnet address. If a match is found, route the packet to thenext hop defined for the IP subnet route.

3) If the subnet check fails, use the default IP network portion basedon the Class A, B, C address for this packet, and look for a route inthe table. If a match is found, route it.

4) If all these checks fail, look for a default entry. 0.0.0.0. If adefault entry exists, route the packet to the next hop defined for thedefault entry.

The route query process of SRP according to the invention can now beexplained. It will be discovered that a default gateway entry can wreakhavoc. If a default gateway entry exists, that path will be taken when aroute fails tests 1-3 above, so the SRP query process will not occur.

One possible solution based on prior art is to run the SRP query processbetween Steps 3 and 4 above. For example, before using the defaultgateway, try to resolve the address using the SRP query process. If thisfails, then use the default gateway. This would work, but has thepotential to generate a sizable amount of SRP queries if the DAMAnetwork is connected to a large IP network, be it the Internet or alarge Intranet.

The SRP according to the invention handles this potential trafficoverload condition through a supernet concept. A supernet is a set of IPnetwork prefixes that are close to each other in terms of prefix in theaddress space, although they need not be contiguous. The networkdesigner configures each IP router with the scope of the search thatshould be done from the address information known by this node. So, ifthis node is aware of 192.168.1.64, subnet mask 26 bits, and thesupernet is set to 24 bits, then this node will try to resolve addressesof 192.168.1.0 using the route query process. If the supernet is set to16 bits, then this node would try to resolve addresses from 192.168.0.0to 192.168.255.255. Note that this spans a number of Class C networks.

Specific Embodiments of SRP

The SRP according to the invention supports the primary function ofbuilding the network map of all directly connected IP network prefixesreachable via the DAMA WAN. Two approaches are provided as examples.

Distance-Vector Approach

Referring to FIG. 8 and FIG. 10, in a Distance Vector Approach, routinginformation is sent at a periodic rate, regardless of whether therouting information has changed. Each ST transmits its basic routinginformation at this periodic rate, and receives basic routinginformation from all other STs at this periodic rate. The NCS acts asthe repeater, transmitting every routing message it receives. Each ST isresponsible for maintaining its own route table, adding routes notalready in its table, refreshing routes already in the table, anddeleting routes if no update has been received after a timeout period.This approach has the following advantages and disadvantages.

Advantages

-   -   1) Simple. Allows for fast high-level design effort.    -   2) Similar to RIPv2. Can reuse existing RIP software.    -   3) Ease of Integration. NCS/ST interaction minimal.

Disadvantages

-   -   1) Wastes control channel bandwidth.    -   2) Does not easily scale to large networks.        Link State Approach

Referring to FIG. 9 and FIG. 11, in a Link State Approach, a singlerouter, called the designated router (DR) keeps a complete routingdatabase of the area. The DR is responsible for updating routers withinthe area as routes are added/deleted and routers are added/deleted.

In one embodiment of the present invention, the NCS serves as the DR. Asthe NCS polls individual STs, it updates a master route database andbroadcasts changes to that database to STs. The NCS will become aware ofroute database mismatches by polling the STs for their route databasechecksums. It can rebroadcast the entire route database if a mismatchoccurs, or have algorithms that checkpoint the database, allowing forincremental updates. This approach has the following advantages anddisadvantages.

Advantages

-   -   1) Scales well for larger networks.    -   2) Efficiently uses control channel bandwidth.    -   3) Algorithm can support extended routing information.

Disadvantages

-   -   1) More complex design.        Scenarios        Remote ST online/offline transition—Distance Vector Approach

Referring to FIG. 8, as remote STs log in and log out of the network, IPnetwork reachability changes must be communicated to the MBR. Note thatin this approach the NCS only sends RIS (add) messages. No RIS (delete)or RIS (summary) messages are sent.

Remote ST Login—The NCS adds this ST to the NCS poll list.

RIN Request—The NCS polls the newly added ST for basic routinginformation.

RIN—The ST sends information regarding its directly connected network.

RIS (add)—The NCS updates its route table and broadcasts only the polledSTs information to the entire network.

Triggered RIP Update—If a gateway ST senses this is a new route, it addsthe route to its table and which triggers a RIP update. If the route isalready in the table a RIP update is not triggered.

RIN Request—The NCS continues polling other nodes in the network, andbroadcasting their responses.

ST Logout—When an ST logs out, the NCS deletes the ST from its pollinglist. No further RIN requests are sent to this ST -> No RINs are sentfrom this ST -> No further RIS (adds) are broadcast for this ST'sroutes. Eventually, the route associated with the logged out ST isdeleted because it does not get refreshed.

Triggered RIP Update—If a gateway ST running RIPv2 deletes this route, aRIP update is triggered (on the terrestrial side of the gateway ST).

Remote ST Online/Offline Transition—Link State Approach

Referring to FIG. 9, as remote STs login and logout of the network, IPnetwork reachability changes must be communicated to the MBR.

Remote ST Login—The ST is added to the NCS poll list.

RIN messages—The NCS periodically polls each ST for basic routinginformation. When a ST enters the network, it has no routinginformation. The NCS detects this when the route database checksum inthe RIN message does not match the checksum the NCS has. This causes theNCS to broadcast the entire routing information database

RIS (all)—The NCS sends out the entire routing information database.This may include multiple messages spread out amongst multipletransmissions. The RIS has a field that informs STs whether this messageincludes the first, middle, or last block of the routing informationdatabase. All STs shall replace their databases with the informationfrom the NCS at this time.

RIN messages—After the network converges to know about the new ST,future RIN poll/responses generate no RIS traffic.

ST Logout—When an ST logs out, the NCS sends out a RIS that instructsall STs to delete routing information pertaining to the ST that justlogged out.

Loss of Communication with Remote ST—Distance Vector Approach

Referring to FIG. 10, the NCS periodically polls STs for basic routinginformation. If the ST does not respond, this causes a routing update tooccur.

RIN Request—The NCS polls each ST for RIN messages. If a ST fails torespond to the polls, the NCS will delete the routing information forthis ST, and continue polling the next node. Since the RIN Request wasunanswered, the NCS will not broadcast a RIS (add) message for thisnode. Eventually, other STs will drop this route from their table ifthey do not receive a RIS (add) message within a route timeout interval.

Triggered RIP Update—If a route timeout occurs on a gateway ST runningRIPv2, a RIP update will be triggered.

RIN Request/RIN—If the non-responsive ST replies to a later RIN Request,the NCS adds the route back to its route table and broadcasts a RIS(add).

Triggered RIP Update—If a gateway ST previously deleted because of aroute timeout, the gateway ST will add the route, and send a RIP update.If the route had not been deleted, its route timeout is simply refreshed(and no triggered RIP update is broadcast).

Loss of Communication with Remote ST—Link State Approach

Referring to FIG. 11, the NCS periodically polls STs for basic routinginformation. If the ST does not respond, this causes a routing update tooccur.

Send RIN—The NCS polls each ST for RIN messages. If a ST fails torespond to three consecutive poll, the NCS deletes the routinginformation for this ST.

RIS (delete)—The NCS sends out a RIS specifying the routes that shouldbe deleted from all ST databases.

RIN response—If the ST later responds to a poll from the NCS (and didn'tgo through the login/logout cycle), the NCS will add the routinginformation for this ST.

RIS (add)—The NCS send out a RIS specifying the routes that should beadded to all ST databases.

Triggered RIP updates—Any changes to the routing information at GatewaySTs cause RIP updates to be sent immediately.

Checksum Does Not Match—Link State Approach Only

Referring to FIG. 12, the NCS retrieves the ST's routing information androuting information database checksums from the RIN poll. If eitherchecksum does not agree with the NCS's, then the ST needs an update.This is not used in the Distance Vector Approach because the DistanceVector Approach does not use checksums

RIN—The NCS polls the ST for routing information. It notes that therouting information database checksum does not agree with the NCS value.This triggers the NCS to broadcast the routing information database.

RIS(all)—The NCS sends out the routing information database to all STs.

TRIN—The NCS polls the ST for routing information. It notes that therouting information database checksum does not agree with the NCS value.This triggers the NCS to broadcast the routing information database.

TRIS(all)—The NCS sends out the routing information database to all STs.

The invention has been explained with reference to specific embodiments.Other embodiments will be evident to those of ordinary skill in the art.It is therefore not intended for this invention to be limited except asindicated by the appended claims.

1-17. (canceled)
 18. A method for establishing routing forcommunications using a satellite in a Demand Assigned Multiple Access(DAMA) Wide Area Network (WAN), the method comprising steps of:receiving Routing Information Messages (RIMs) from a plurality ofsubscriber terminal (ST) nodes at a Network Control Station (NCS);constructing a network map of Internet protocol (IP) network prefixesreachable via the DAMA WAN, wherein the network map is constructed usingthe RIMs; allocating a bandwidth constricted control channel using thesatellite; and sending at least one control channel message over thebandwidth constricted control channel to at least one ST node coupled tothe WAN.
 19. The method for establishing routing for communicationsusing the satellite in the DAMA WAN as recited in claim 18, wherein thecontrol channel message includes information related to the network map.20. The method for establishing routing for communications using thesatellite in the DAMA WAN as recited in claim 18, wherein the NCScommunicates with the plurality of ST nodes in a hub-and-spoke manner.21. The method for establishing routing for communications using thesatellite in the DAMA WAN as recited in claim 18, further comprising astep of periodically transmitting routing information whether or not therouting information has changed for the ST node.
 22. The method forestablishing routing for communications using the satellite in the DAMAWAN as recited in claim 18, wherein at least one of the plurality of STnodes performs a step of providing routing information beyond the one'sdirectly-connected network.
 23. The method for establishing routing forcommunications using the satellite in the DAMA WAN as recited in claim18, wherein the constructing step comprises a step of constructing thenetwork map at the NCS.
 24. The method for establishing routing forcommunications using the satellite in the DAMA WAN as recited in claim18, further comprising steps of polling at least one of the plurality ofST nodes to solicit a RIM.
 25. The method for establishing routing forcommunications using the satellite in the DAMA WAN as recited in claim18, further comprising steps of: determining if the network map of theat least one ST node is out of date; and sending at least some of thenetwork map to the at least one ST node when the network map is out ofdate.
 26. The method for establishing routing for communications usingthe satellite in the DAMA WAN as recited in claim 18, wherein thecontrol channel message includes changes to the network map.
 27. Amethod for establishing routing for communications using a satellite ina Demand Assigned Multiple Access (DAMA) network, the method comprisingsteps of: receiving a first Routing Information Message (RIM) from afirst subscriber terminal (ST) node at a Network Control Station (NCS);receiving a second RIM from a second ST node at the NCS; constructing anetwork map of Internet protocol (IP) network prefixes reachable via theDAMA network, wherein the network map is constructed using the first andsecond RIMs; allocating a bandwidth constricted control channel usingthe satellite; and sending at least one control channel message over thebandwidth constricted control channel to a third ST node coupled to theDAMA network, wherein the at least one control channel message includesinformation related to the network map.
 28. The method for establishingrouting for communications using the satellite in the DAMA network asrecited in claim 26, further comprising steps of: detecting when thesecond ST node is no longer available to the DAMA network; and removingthe second ST node from the network map.
 29. The method for establishingrouting for communications using the satellite in the DAMA network asrecited in claim 26, further comprising steps of: polling the third STnode; determining the third ST node has an old network map; and sendingthe third ST node the network map based upon the determining step. 30.The method for establishing routing for communications using thesatellite in the DAMA network as recited in claim 26, wherein the NCScommunicates with the first, second and third ST nodes in ahub-and-spoke manner.
 31. The method for establishing routing forcommunications using the satellite in the DAMA network as recited inclaim 26, further comprising a step of polling the first and second STnodes, wherein the first and second RIMs are received in response to thepolling step.
 32. The method for establishing routing for communicationsusing the satellite in the DAMA network as recited in claim 26, whereinthe constructing step comprises a step of constructing the network mapat the NCS.
 33. A Demand Assigned Multiple Access (DAMA) network thatestablishes a network map used for satellite communication, the DAMAnetwork comprising: a plurality of subscriber terminal (ST) nodes,wherein the ST nodes produce Routing Information Messages (RIMs); aNetwork Control Station (NCS) that receives the RIMs for use inconstructing the network map of Internet protocol (IP) network prefixesreachable via the DAMA network; and a bandwidth constricted controlchannel allocated using the satellite, wherein at least one controlchannel message is sent over the bandwidth constricted control channelto at least one ST node coupled to the network.
 34. The DAMA networkthat establishes the network map for satellite communication as recitedin claim 32, wherein packets from a public terrestrial network arerouted to traverse the DAMA network.
 35. The DAMA network thatestablishes the network map for satellite communication as recited inclaim 32, wherein the at least one ST node is a stub network.
 36. TheDAMA network that establishes the network map for satellitecommunication as recited in claim 32, wherein the control channelmessage includes the network map.
 37. The DAMA network that establishesthe network map for satellite communication as recited in claim 32,wherein the network map is sent to the at least one ST node in a numberof messages.
 38. The DAMA network that establishes the network map forsatellite communication as recited in claim 32, wherein the NCSCommunicates with the plurality ST nodes in a hub-and-spoke manner.